Heated Tool Butt-Welding (PE-HD & PP) SABS0268

-fusion jointing is a thermofusion process which involves the simultaneous heating of the ends of two components which are to be joined until a melt state is attained on each contact surface. The two surfaces are then brought together under controlled pressure for a specific cooling time and homogeneous fusion is formed upon cooling. The resultant joint is resistant to end thrust and has comparable performance under pressure to the pipe.

 

This method of jointing requires an electrically heated plate to raise the temperature of the pipe ends to the required fusion temperature and is used for PE 63, PE 80 and PE 100 grades of material for pipe of size 32 mm and above of the same Standard Dimension Ratio (SDR). When joining pipes using butt-fusion techniques, the heater plate temperatures are the same for PE 63, PE 80 and PE 100, 195 °C to 200 °C

 

The Site Fusion Jointing Specification WIS 4-32-08 Issue 2, 1994 emphasises the importance for the butt-fusion machine to be able to control the reduced secondary ram pressures that are now required for dual pressure butt-fusion jointing. For SDR 11 pipes of sizes 250 mm, 280 mm and 315 mm and for all pipe (SDRs 11, 17.6, 26) of size 355 mm and above the butt fusion pressures should be reduced after 10 seconds and therefore the use of an automatic butt fusion machine is required.

Equipment Required

• All welding is done as per SABS 4427.
• Approved Butt-Welding Machine (inclusive of trimmer), Heated Plate and Hydraulic Pump.
• Generator
• Welding Tent
• Pipe Support Rollers
• Clean Water or Clear Spirits Lint free cloths
• External/Internal De-beading tool
• Bead Gauge
• Pipe end-covers
• Marker Pens
• Pipe Cutting Tools
• Digital Thermometer (Calibrated)

Butt-welding Procedure

• All welding is done as per SABS 4427.
• Set up the equipment. If necessary, erect a welding tent to protect against wind and dust.
• Mount the facing planer (trimmer).
• Align the pipe ends or parts to be welded with the aid of roller mountings or other supports. (Never attempt to weld together pipes with different SDR ratings).
• Clamp the pipe or parts and seal the ends. Trim/plane the joint faces.
• Remove the planer and excess shavings. Take care not to touch joints face by hand.
• Check for pipe alignment radially; by bringing the joint faces together. (Max Gap = 0.5mm).
• Check for pipe alignment axially in line with wall thickness. (Max = 0.1/s-s {wall thickness} ).
• Clean the area of the heating plate with lint free cloth and water/clear spirits.
• Check the welding temperature. (195°C +/-10°C)
• Insert the heated plate.
• Exert the heating pressure by the hydraulic unit until a bead is formed along the circumference of the joint faces.
• Reduce pressure to allow for heat dissipation into wall of pipe axially. (Soaking period).
• Remove heating plate over the allocated time and immediately join the molten joint faces together, ensuring that the change-over time is not exceeded.
• Steadily increase the welding pressure to its allocated value.
• Keep at this pressure for the allocated time.
• Allow for cooling down at the welding pressure over the allocated time.
(Never remove a weld from the machine before the cooling time has elapsed).
• When this cooling time has elapsed, reduce pressure to 0 and remove welded joint from clamps.